Graft copolymers of polyolefins and acrylic and methacrylic acid and method of making the same



United States Patent GRAFT CGPOLYMERS 0F POLYOLEFINS AND ACRYLIC ANDNETHACRYLIC ACID AND METHOD OF MAKING THE SAME Robert M. Nowak andGiflin D. Jones, Midland, Mich, assignors to The Dow Chemical Company,Midland,

Mich, a corporation of Delaware No Drawing. Filed Get. 10, 1960, Ser.No. 61,357

8 Claims. (Cl. 260- 878) This invention concerns a method of makinggraft copolymers comprising polyolefins and acrylic acid and/ ormethacrylic acid, and pertains to compositions comprising the graftcopolymer and homopolymers and copolymers of said acids. It relates moreparticularly to an improved method for making such graft copolymers andpertains to the graft copolymer products.

It is known to prepare polymeric products by subjecting a mixture of apolymerizable monomeric olefinic compound and a linear polymer in theabsence of oxygen to an agitation treatment suflicient to degrade thelinear polymer and thereby yield a polymer in the molecular structure ofwhich the olefinic compound forms a part.

It is known to prepare polymeric products comprising graft copolymers byfor example, polymerizing a monomer in the presence of, or in admixturewith, a latex of an already formed polymer in an aqueous emulsion and inthe presence or absence of an added polymerization catalyst.

It has now been discovered that graft copolymers of normally solidthermoplastic resinous homo-polymers and copolymers of one or morealiphatic olefins containing from 2 to 4 carbon atoms in the moleculeand copolymers containing a predominant amount of one or more of suchaliphatic ol'efins chemically combined or interpolymerized in thecopolymer molecules can readily be pre pared in good yield and in pureor substantially pure graft copolymer form by a procedure which consistsessentially of malaxing the normally solid thermoplastic olefin polymerat elevated heat-plastifying temperatures between ll0 and 250 C; whilecontacting the heat-softened or molten polymer with a minor proportion,i.e. 50 percent by weight or less of the total mixture, of acrylic acid,methacrylic acid or a mixture of such acids having dissolved thereinfrom 0.04 to 5 percent by weight of a peroxygen compound having ahalf-life of at least 15 minutes determined by its decomposition rate inbenzene at 100 C.

It is important that the malaxing, i.e. the kneading, rubbing, mixing orstirring, of the heat-plastified or molten polymer in contact with themonomer containing the peroxygen compound, be carried out in such manneras to avoid appreciable breakdown or degrading of the polymer moleculessuch as by carrying out the malaxing in a plastics screw type extruderor a Banbury mixer.

It has fucther been found that by malaxing the heatsoftened or moltenpolymer with the monomeric acid containing the peroxygen compounddissolved therein that there appears to be formed a large number ofgrafting sites along the polymer chains with the resultant formation ofgraft copolymers consisting predominantly of the substrate polymerhaving attached thereto a large number of grafted-on chains of themonomeric acid units of relatively short chain length. Such polymers areunique, and difler in their chemical composition and properties fromgraft copolymers consisting of substrate polymers having relatively fewgrafted-on chains of monomer units of long chain length, but ofotherwise similar chemical composition.

, The polymeric substrate to be employed in preparing the graftcopolymers is preferably a homopolymer or coice polymer of one or morealiphatic olefins containing from two to four carbon atoms in themolecule such as polyethylene, polypropylene, polyisobutylene,polybutene, copolymers of ethylene and propylene, copolymers of ethyleneand isobutylene, or copolymers of ethylene and butene, althoughcopolymers containing a predominant amount, i.e. 50 percent by weight ormore, of one or more of the aliphatic olefins chemically combined orinterpolymerized with a minor proportion of another monoethylenicallyunsaturated organic compound can be used,

such as ccp olyrners of a predominant amount by weight of ethylene and aminor proportion of styrene, vinyl acetate, or methyl methacrylate.

The monomers to be graft polymerized onto the polymeric substrate can beacrylic acid, methacrylic acid or mixtures of said acids. in any and allproportions. The monomeric acid is employed in' amounts corresponding tofrom 1 to 100, preferably from about 5 to about 50 parts by weight perparts by weight of the polymer starting material, and preferablycontaining a polymerization inhibitor such as tert-butyl catechol,hydroquinone or monomethyl ether of hydroquinone in amounts of about0.02 percent by weight, but an inhibitor is not required.

The organic peroxygen compound to be employed as the agent forinitiating the graft copolymerization reaction between the monomericacid and the polymer starting material at the elevated heat-plastifyingtemperatures at which the reacting is carried out can be any organicperoxygen compound which is a polymerization catalyst for the monomericacid and has a half-life of at least 15 minutes as determined by itsdecomposition rate in benzene at 100 C. Among suitable organic peroxygencompounds are tent-butyl peracetate, ter-t.-butyl perbenzoate,di-tert.-buty1 diperphthalate, tert-butyl hydroperonide, di-tent-butylperoxide, cumene hydroperoxide, dicumyl peroxide, ben-zoyl peroxide, andthe like. Mixtures of any two or more of the organic peroxygen compoundscan be used. The organic peroxygen compound can be used in amountscorresponding to from 0.04 to 5 percent by weight of the monomeric acid.

A method of determining the heat stability of organic peroxides has beendescribed by D. F. Doehnert and Q. L. Mageli, The Society of PlasticsIndustry Inc. (preliminary copy of a report to be presented at the 13thannual meeting of the Reinforced Plastics Division, Chicago, Illinois).

In practice, the polymer, e.g. polyethylene or polypropylene in the formof molding powder or granules, is fed to a plastics extruder wherein itis pressed and heated to a fiowable or molten condition at temperaturesbetween and 250 C., and above the crystalline melting point of thepolymer, under pressure. The monomeric acrylic acid or methacrylic acid,or a mixture thereof containing the organic peroxygen compound dissolvedtherein is fed under pressure into a mid-section of the barrel of theextruder and into contact with the heat-plastified or molten polymer.The resulting mixture is maintained molten or fiowable and is blendedinto a homogeneous composition as it is forwarded by action of the screwin the barrel of the plastics extruder toward the discharge orifice ordie. During contact and blending of the monomeric acid containing theperoxygen compound with the heat-plastified polymer at the elevatedtemperatures, the peroxygen compound undergoes decomposition withresultant initiating of a polymerization reaction and the formation of agraft copolymer. The monomeric acid and the molten or heat-plastifiedpolymer are maintained in contact with one another at the elevatedtemperatures for a time sufiicient to polymerize all or substantiallyall of the monomers, then is extruded and cooled and cut or ground to agranular form. In an alternate procedure the heat-plastified polymer andthe monomeric acid are maintained in contactwith one another at theelevated reaction temperatures until at least a predominant amount ofthe monomeric acid is' polymerized, then is extruded, cooled and thegraft copolymer separated from the reacted mixture.

The graft copolymer is recovered in pure-r substantially pure form bydissolving the graft copolymer in a solvent in which the homopolymer isinsoluble such'as toluene, xylene, ethylbenzene, isopropylbenzene andthe like, filtering the solution to separate theinsoluble material andrecovering the graft copolymer from the, filtrate in usual ways, eg.by'precipitating the graft copolymer I with methanol andseparating,Washing and drying the graft copolymer. V v

The new graft copolymers are useful for a variety of purposes. They canbe molded'by usual compression and injection molding operations or byextrusion methods.

to form useful articles, such as boxes, cups, trays, or

may contain from 1 to 50, preferablyfromabout 5 to V as stated in thefollowing table. 7

acrylic acid and the heat-pla'stified polyethylene uwas rods, bars,sheet or film material; The graft copolymers percent by weight of theacrylic acid "or methacrylic acid chemically combined with the polymericsubstrate starting material. The graft copolymers possess goodmechanical properties .such as tensile strcngth, percent elongation andfluxural modulus, and in general possess EXA PLE 2' In each of a seriesof'experiments, polyethylene having 0 a melt index of 2 was fed to a 2/2 inch screw diameter Welding Engineers plastics extruderyat' a rate of50 pounds per hour wherein the polyethylene was pressed, heated attemperaturesof from 185 to 200. C. and was mixed with acrylic containing0.02 percent byweight of tert.-butyl catechol asinhibitor and 1 percentby weight ofdicumyl peroxide as .interpolymerization catalyst, also fedto the barrel of the extruder at a rate sufficient to form a compositionor graft copolymer containing chemical combined or interpolymerizedacrylic'acid in amount The mixture of the blended under'pressure inthelplastics extruder attemp eratures between- 185 and 200 C. for aperiod of 5 minutes, then was extrudedythrough an orifice into theatmosphere and was cooled and ground to a'granular, form suitable formolding. The'graft copolymer prod not was recovered employing proceduresimilar'to that employed in Example 1. Molded test pieces of the graftcopolymer product were used to determine the tensile improvement in oneor more of such properties over the similiarproperties for the polymericsubstrate starting material.

The following examples illustrate ways in which the principle of theinvention has been applied, but are not to be construed as limiting itsscope.

EXAMPLE 1 Polyethylene having a melt index of 2 and in granular form wasfed to a 1% inch diameter screw type plastics extruder at a rate of 24.5grams per minute wherein it was pressed and heated to a molten conditionunder pressure at a temperature of about 190 C. The molten polyethyleneunder pressure was mixed with monomeric acrylic acid containing 0.04percent by weight of tert.-y

butyl catechol as polymerization inhibitor for the monorner at ordinarytemperatures and'0.75 percent by weight of tert.-butyl peracetate ascatalyst for initiating interpolymerization of the monomeric acrylicacid withthe heatplastified polyethylene at the elevated temperatures,which monomeric acrylic acid Was fed to a mid-section of theextruder'barre'l at a rate of 3 grams per minute.

The resulting mixture was heated and mixed in the extruder barrel attemperatures of about 190 C. for a period of about 2.5 minutes, then wasextruded through an orifice into the atmosphere wherein it was cooledand was cut to a granular form. Portions of the graft copolymer wereinjection molded to form test pieces of A; x inch cross-section. Thesetest pieces were used to determine'the tensile strength andpercentelongation forthe graft copolymer employing procedures similar to thosedescribed in ASTM D638-49T. Other portions of the product were used todetermine thepercent by weight of acrylic acid chemically combined orinterpolymerized with the polyethylene starting material, and thepercent of volatile material in the graft copolymer. The

product was substantially pure graft copolymer having the properties setforth under A below. For comparison, the properties of the polyethylenestarting material are set forth under B.

Graft Polyethylene copolymer Melt Index 0. 5 2 Acrylic Acid 9 TensileStrength 1, 670 1 1, 480 Elongation. 180 15 Volatile -1-.. 0.5

1 Lbs/sq. in.

strength andpercent elongation for the composition employing proceduresimilar to that described in ASTM D638- 49T. Other portions of thecomposition were tested forimelt index, employing procedure similar tothat described in ASTM Dl238-57T, and for'percent volatiles.

Table I identifies the compositions by giving the proportions ofpolyethylene and acrylicQacidusediri preparing the same. The table also:gives the properties determined for the composition. For comparison theproperties of the polyethylene arealso given inthe table as Run No. 1. ia

Table I 7 Starting Materials Product Run a V No. Poly- Acrylic MeltTensile Elonga- Volatiles,

. ethylene, Acid, Index' Strength, tion, percent percent percentlbsl/sq. in. percent V EXAMPLE 3 By procedure similar to that describedin Example 2,

granular polypropylene was fed to the plastics extruder andmixed withacrylic acid containing 2' percent by Weight of dicumylperoXide,.in-proportions as stated in the following table. Themixture ofthe acrylic acid and the polypropylene Was blended in the extruderunder.

pressure at temperatures between and 200 C. for

about 30 seconds,,then wasextruded, cooled 'and was ground to a granularform. Table II identifies thecompositions and gives the propertiesdetermined for said compositions.

In each of a series of ,experimentspolyethylene having a melt index of 2was fed to a plastics extruder wherein it was blended with acrylic acidin proportions as stated in the .following'table the presence of anorganic employed in Example 1. Table III identifies the experiments,names the peroxide used and gives the properties determined for thecompositions.

200 C. for a time of about 3 minutes, then was extruded into theatmosphere. The extruded material was devolatilized by heating the sameunder subatmospheric pressure then was cooled and crushed to a granularform. The product was analyzed and was found to contain 4.5

Table III Starting Material Product Run No.

Poly- Acrylic Melt Per- Tensile Elonga- Melt ethylene, Acid, IndexOrganic Peroxide, Kind cent Strength, tion, Index percent percentlbs/sq. in. percent 100 2 None 1, 480 157 2 94 6 2 Tort-butylhydroperoxide a 1 1, 660 169 1. 2 93 7 2 Di-tert-butyl peroxide 1 1, 630170 1. 6 93 7 2 Tert.-butyl perbenzoate 1 1, 690 161 1. 6 03 7 2 Methylethyl ketone peroxide 1 1, 680 165 1. 1 93 7 2 Cumene hydroperoxide. 11, 628 163 1. 6 93 7 2 Benzoyl peroxide 1 1, 673 175 1. 4 91 9 2Tert.-butyl peracetate 1 1, 610 170 0. 9

EXAMPLE percent by weight of chemically combined acrylic acid.

In each of a series of experiments, polypropylene having a melt index of0.9 was fed to a plastics extruder wherein it was blended with acrylicacid containing tert.- butyl catechol and tort-butyl peracetate, and inproportions as stated in the following table employing an apparatus andprocedure similar to that employed in Example 1. Table IV identifies theexperiments and gives the properties determined for the composition.

Table IV Starting Materials Product Run No.

Tensile Stren gth lbs/sq. in.

Acrylic Acid Percent Polypropylene, Percent Elongation percent EXAMPLE 6EXAMPLE 8 Polyethylene having a melt index of 2 was fed to a 1% inchdiameter screw type extruder at a rate of 23 grams per minute wherein itwas heated and blended under pressure with methacrylic acid containing0.02 percent by weight of tert.-butyl catechol and 1 percent of dicumylperoxide, which methacrylic acid was fed to the barrel of the extruderat a rate of about 3 grams per minute. The resulting mixture was blendedunder pressure in the barrel of the extruder at temperatures up to 180C. for a period of about 2.5 minutes then was extruded into theatmosphere, was cooled and was cut to a granular form. The product washeated at 95 C. under an absolute pressure of from 2-5 millimeters toremove volatile ingredients, then was cooled. The devolatilized productwas analyzed and was found to have a melt index of 1.6 and to contain 8percent by weight of chemically. combined methacrylic acid. It was agraft copolymer.

EXAMPLE 9 A charge of 1500 grams of polyethylene having a melt index of20 was placed in a Baker-Perkins type mixer, purged with nitrogen gas,and was mixed and heated to 135 C. Thereafter, there was added slowlywith mixing 170 grams of acrylic acid containing 0.1 ml. of di-tert.-butyl peroxide, over a period of minutes. The resulting mixture wasblended at 135 C. for one hour, then was removed from the mixer and wasallowed to cool to Table V Starting Material Product Run No.

Poly- Acrylic Dicumyl Yield Elongation, Melt ethylene, Acid, Peroxide,Strength, Percent Index Percent Percent Percent lbs/sq. in.

EXAMPLE 7 room temperature. There was obtained 1645 grams of A copolymerof 95 mole percent propylene and 5 mole percent ethylene containing 0.1percent by weight of 2,6-di-tert.-butyl-4-methyl phenol as antioxidantwas fed to a 1% inch diameter screw type extruder at a rate of 15 gramsper minute, wherein it was heated and was mixed with acrylic acidcontaining 0.02 percent by weight of by droquinone monomethyl ether and1 percent of dicumyl peroxide, also fed to the extruder at a rate of 1gram per minute. The resulting mixture was blended under pressure in thebarrel of the extruder at temperatures up to graft copolymer containing9 percent by weight of chemically combined acrylic acid. The product wassoluble in boiling toluene.

We claim:

1. A method for making a graft copolymer which comprises malaxating anormally solid resinous thermoplastic polymer selected from the groupconsisting of (a) homopolymers of aliphatic olefins containing from 2 to4 carbon atoms in the molecule and (b) copolymers consisting of at leasttwo interpolymerized aliphatic olefins containing from 2 to 4 carbonatoms in the molecule, at heatwhile contacting the heat-softened polymerwith a monomfer selected from the group consistingof acrylic acid andmethacrylic acid having dissolved therein from 0.04 to- 5 percent byweight of an organic peroxygen compound having a half-life'of at least15 minutes as determined in' benzene vat 100 C., and in amountcorrespondingto'fromabout 1 to 100 parts by Weight of said monomer per100 parts by weight of the heat-softened polymer, forga time sufficientto polymerize substantially all of the monomer.

2.7A method for making a graft copolymer which comprises malaxating anormallysolidresinous thermoplastic polymer selected from the groupconsisting of (a) homopolymers. of aliphatic olefins containing from'2.to-4 Carbon atoms in, the molecule and (b) copolymers consisting V ofat least two interpolymerized aliphatic olefins containing f1'om2 to 4carbon atoms in the molecule, at heat-. plastifying temperatures between110 and 250 C. which" avoids appreciable deterioration of. the polymermolecules while contacting the'heat-softened polymer with a mono merselected from the group consisting of acrylic acid and methacrylic acidhaving dissolved therein from 0.04 tov 5 percent by weight of anorganicperoxygen compound having a half-life of at least 15 minutes asdetermined in benzene at 100 C. and in amount corresponding to from 1 tolparts by Weight of said monomer per 100 parts by weight of theheat-softened polymer. for a time sufficient 1 to polymerize at least apredominant amount of said monomer and thereafter separating the graftcopolymer from.

the reacted mixture. V

3. A method according to claim 2,Wherein the polymer is polyethylene.

4. A method according to claim 2, whereinthe monomer is acrylic acid.

5. A method according to claim 2, wherein thepolymer is polypropylene.

6. A method according to claim 2, wherein the monomer is methacrylicacid.

7. A method'for making a graft copolymer which 8 comprisesirralaxatingpolyethylene at heat-plastifying temperaturesbetweeh; 110 and 250 whichavoids appreciable deterioration of thep'olymer trnolecules whilecontacting the heat-softened polyethylene with acrylic acid containingfrom 0.04 to 5 percent by'weight of an organic peroxygen compound.having .a' half-life of at least 15 minutes as determined inbenzene at100 C. ,and in amount corresponding to from 1 to 100 parts by weight ofthe acrylic acid per. 100 parts by weight of the heat:softenedpolyethylenc for a time sufiicient to polymerize at least apredominant amount of the acrylic acid and thereaftersepar-ating thegraft copolymer from the reacted mixture. a

8. A method for making a graft. copolymer which comprises malaxatingpolypropylene at heat-plastifying temperatures between 110 and 250. C.which avoids appreciable deterioration of the polymer moleculeswhilecontac'ting the heat-softened polypropylene with methacrylic acid Ihaving from 0.04'tor5'percent by weight of an organic .20 perorrygencompound having a halfdife" of-at least 15 minutes as determined in;benzene at C. and in amount corresponding to from 1; to 100 parts byweight of the methacrylic acid per lOQ parts by weight of theheatsoftened polypropylene for a time sufficient to polymerize V atleast a predominant amount ofthe methaci'ylic acid and thereafterseparating the graft copolymer from the reacted mixture. Y i

References Cited by'the Examiner UNITED STATES PATENTS 1/61 Rugg a a1.260-878 FOREIGN PATENTS 1/5 9 Australia. 9/52 Great Britain. 6/59 GreatBritain.

LEGN J. BERCOVIT Z, Primary Exarriiner; 4O

1. A METHOD FOR MAKING A GRAFT COPOLYMER WHICH COMPRISES MALAXATING ANORMALLY SOLID RESINOUS THERMOPLASTIC POLYMER SELECTED FROM THE GROUPCONSISTING OF (A) HOMOPOLYMERS OF ALIPHATIC OLEFINS CONTAINING FROM 2 TO4 CARBON ATOMS IN THE MOLECULE AND (B) COPOLYMERS CONSISTING OF AT LEASTTWO INTERPOLYMERIZED ALIPHATIC OLEFINS CONTAINING FROM 2 TO 4 CARBONATOMS IN THE MLECULE, AT HEATPLASTIFYING TEMPERATURES BETWEEN 110* AND250*C., WHICH AVOIDS APPRECIABLE DETERIORATION OF THE POLYMER MOLECULES,WHILE CONTACTING THE HEAT-SOFTENED POLYMER WITH A MONOMER SELECTED FROMTHE GROUP CONSISTING OF ACRYLIC ACID AND METHACRYLIC ACID HAVINGDISSOLVED THEREIN FROM 0.04 TO 5 PERCENT BY WEIGHT OF AN ORGANICPEROXYGEN COMPOUND HAVING A HALF-LIFE OF AT LEAST 15 MINUTES ASDETERMINED IN BENZENE AT 100*C., AND IN AMOUNT CORRESPONDING TO FROMABOUT 1 TO 100 PARTS BY WEIGHT OF SAID MONOMER PER 100 PARTS BY WEIGHTOF THE HEAT-SOFTENED POLYMER, FOR A TIME SUFFICIENT TO POLYMERIZESUBSTANTIALLY ALL OF THE MONOMER.